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Criticality of Low Enrichment Uranium in Hydrogen

C. B. Mills, G. I. Bell

Nuclear Science and Engineering

Volume 12 / Number 4 / April 1962 / Pages 469-473

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In this paper we present calculated critical masses of homogeneous water-moderated assemblies containing low enrichment uranium. The calculations were made using the multigroup DSN code with eighteen energy groups. Effective absorption cross sections for U238 were computed with the “infinite mass” and “narrow resonance” approximations. The calculations have been compared with various experiments and rather good agreement was found. The results are presented as a parametric survey for U235/U atom ratios from 0.014 to 0.300 and for all H/U235 ratios for which criticality is possible. The decrease in critical radius with an infinite water reflector is also shown. We find that a bare homogeneous system with U235/U < 0.010 cannot be made critical at any H/U235 ratio.